The present invention relates to a device for loading catalyst or other pellets, and especially for loading pellets into the vertical reactor tubes of a chemical reactor.
Many chemical reactors are essentially a large shell and tube heat exchanger vessel, with the reaction occurring inside the tubes and a coolant circulating in the vessel outside the tubes. A chemical reactor vessel also can be a simple tank with a single volume of catalyst inside it, or it may be a single large tube. Some chemical reactions occur in furnace or reformer tubes, which may be a part of a system with 10 to 5000 or more such tubes. In any of these reactor vessels, catalyst, typically in the form of pellets (and other types of pellets that are not catalyst such as inert material or inert pellets), may be loaded into the reactor to facilitate the reaction. The pellets are replaced periodically.
The reactor tubes may be quite long, housed in a structure several stories tall, and the pellets may be transported up several stories to an elevation above the top of the tubes so they may then flow by gravity into the tubes. The pellets typically are supplied in 2,000 pound (or larger) “super sacks”, 55 gallon drums, mini drums, metal bins or plastic bags loaded in pallet-mounted cardboard boxes.
The pellets are then carefully loaded into each reactor tube (there may be several thousand tubes in a single reactor) to try to uniformly fill each tube. In some applications, each tube may be 40 feet long or longer and the customer may wish to load the tubes with a particular loading profile. For instance, the customer may wish to have a 12 to 18 inch layer of inert pellets at the bottom of each tube followed by a layer several feet thick of catalyst A, then a second layer of inert pellets of a given height, and finally a layer several feet thick of catalyst B.
In the prior art, the operator loading the pellets into the reactor tubes loads a few pellets into the tube and then inserts a long tape or rod down the tube to determine the level of the pellets in the tube. If the pellet level is too low, he pulls the tape or rod out of the tube, loads a few more pellets into the tube and repeats the operation until he finally ensures that the pellets have reached the correct height in the tube. Since this is a very cumbersome and time-consuming process, the operator often takes shortcuts, such as adding too many pellets before taking a new reading of the height in the tube. If he overshoots the level (and when taking the shortcut he will eventually overshoot the desired height in a tube), he has to try to remove some of the excess pellets, which can be an ordeal when trying to vacuum pellets that are 40 feet down inside the tube.
Furthermore, it takes time to drop the tape or rod down the tube and then pick it back up every time he needs to check the level of the pellets in the tube. The operator then tends to drop the rod down into the tube to save time, but in the process he smashes the catalyst pellets already in the tube, damaging the catalyst pellets and generating unwanted dust, both of which negatively impact the pressure drop across the tube and the performance of the catalyst.